Optical node device, optical network controller, and optical network control method

ABSTRACT

In an optical network based on a dense wavelength division multiplexing system using a flexible frequency grid, it is difficult to improve the usage efficiency of an optical frequency band owing to the occurrence of fragmentation of the optical frequency band; therefore, an optical network controller according to an exemplary aspect of the present invention includes an optical frequency region setting means for dividing an optical frequency band used in an optical network based on a dense wavelength division multiplexing system using a flexible frequency grid, and setting a plurality of optical frequency regions; and an optical path setting means for setting optical paths having a common attribute in at least one of the plurality of optical frequency regions.

TECHNICAL FIELD

The present invention relates to optical node devices, optical networkcontrollers, and optical network control methods, in particular, to anoptical node device, an optical network controller, and an opticalnetwork control method that are used in an optical network based on adense wavelength division multiplexing system using a flexible frequencygrid.

BACKGROUND ART

A current challenge for optical communications is to expand thecapacities of optical backbone network to cope with the possible futureexplosive expansion of information communications traffic. Variousapproaches are being taken to the challenge. One of the approaches is tocarry out research and development regarding an improvement in usageefficiency of an optical frequency band.

In optical networks, optical frequency bands are used in accordance withthe Dense Wavelength Division Multiplexing (DWDM) system standardized bythe Telecommunication Standardization sector of the InternationalTelecommunication Union (ITU-T). In the DWDM system, the entireavailable optical frequency band is divided into narrow segments by agrid with constant width, called a wavelength grid, and optical signalsin one wavelength channel are allocated within a grid spacing (ITU-Trecommendation G.694.1).

In a flexible frequency grid that is standardized by ITU-Trecommendation G.694.1, the minimum channel spacing is set at 12.5 GHzinstead of 50 GHz used conventionally, and a frequency slot width isvariable by 12.5 GHz. This makes it possible to allocate a frequencyslot of different widths to each optical path; accordingly, it becomespossible to minimize an optical bandwidth to be allocated to an opticalpath.

That is to say, the flexible frequency grid enables to allocate anoptical bandwidth only as needed. Specifically, for example, it is onlynecessary in the flexible frequency grid to allocate an opticalbandwidth of 12.5 GHz if the required optical bandwidth is equal to 12.5GHz and to allocate an optical bandwidth of 50 GHz if it is equal to 50GHz. In contrast, in a fixed grid before the introduction of theflexible frequency grid, if the frequency slot width is set at 50 GHz,an optical bandwidth of 50 GHz is allocated equally to each optical pathregardless of a required optical bandwidth. Even though a requiredoptical bandwidth is 12.5 GHz, for example, the optical bandwidth to beallocated is 50 GHz; accordingly, a bandwidth by 37.5 GHz is allocatedin vain. In contrast, the flexible frequency grid makes it possible toreduce such unnecessary allocation of the bandwidth, so it enables theoptical frequency band usage efficiency to improve.

However, even though the flexible frequency grid is used, an unusedfrequency region can arise, and a fragmentation of the optical bandwidthallocation may arise. It is considered that an optical path with fourslots in width is intended to be generated and there are ten empty slotsas a whole in the optical frequency band of an optical fiber, forexample. If the ten empty slots are composed of five pairs of emptyslots each of which includes two consecutive slots, it is impossible togenerate an optical path with four slots in width. That is to say,despite the fact that there are sufficient empty slots in total, it isimpossible to secure consecutive empty slots because the respectiveempty slots are disposed in fragments. As a result, the situation mayoccur where it is impossible to allocate to an optical path a wideoptical bandwidth with which high-capacity or long-distancecommunications can be achieved. This is called a fragmentation of anoptical frequency, which is made easier to arise as the center opticalfrequency of the optical path or the number of slots of the opticalbandwidth is changed more repeatedly.

Patent Literature 1 discloses a technology to solve the above-mentionedproblem that the fragmentation of the optical frequency arises.

In a method for eliminating the fragmentation of an optical spectrum inan optical network described in Patent Literature 1, first, opticalsignals are allocated to a plurality of frequency slots. This allocationis performed based on a first-fit algorithm of searching firstunoccupied consecutive frequency slots closest to a selected frequencyslot. In this case, a frequency slot dependency map is created based onthe allocation of a plurality of optical signals to a plurality offrequency slots. The frequency slot dependency map relates groupsincluding one or more frequency slots allocated to different opticalsignals interdependently.

If an optical signal departure event that an optical signal is droppedfrom an optical network occurs, a frequency slot occupied by the opticalsignal is released as a result. The optical signal departure event andthe release of frequency slots cause fragmentation of the opticalspectrum of the optical network.

In the method for eliminating fragmentation of optical spectrumdescribed in Patent Literature 1, the fragmentation of the opticalspectrum is eliminated by reallocating optical signals to differentfrequency slots based on the frequency slot dependency map. That is tosay, by using the frequency slot dependency map after an optical signaldeparture event, frequency slots of one or more optical signalsdepending on a frequency slot of a dropped optical signal aredetermined. Based on that information, an optical signal is reallocatedto a frequency slot released by the departure of the dropped opticalsignal (defragmentation).

There are related technologies described in Patent Literature 2 andPatent Literature 3.

CITATION LIST Patent Literature

-   [PTL 1] Japanese Patent Application Laid-open Publication No.    2013-223245 (paragraphs [0021] to [0048])-   [PTL 2] Japanese Patent Application Laid-open Publication No.    H06-252867-   [PTL 3] Japanese Patent Application Laid-open Publication No.    2008-227556

SUMMARY OF INVENTION Technical Problem

In the above-mentioned method for eliminating fragmentation of opticalspectrum described in Patent Literature 1, the fragmentation of theoptical spectrum is eliminated by reallocating optical signals todifferent frequency slots based on the frequency slot dependency map(defragmentation). However, it is difficult to perform thedefragmentation of the optical frequency band with all the opticalsignals uninterrupted instantaneously. The reason is as follows.

It is necessary to change an optical frequency of an optical signal inan optical transmitter and receiver in order to perform thedefragmentation of an optical frequency band. However, it takes a timefrom several seconds to several tens of seconds in the presentcircumstances to change the optical frequency, to stabilize the opticalfrequency, and to enable the optical transmitter and receiver to launchits service.

If the defragmentation of the optical frequency band is performed,therefore, communication services are suspended in the interveningperiod. Since the interruption in communication services takes away fromuser's convenience remarkably, it is difficult to perform thedefragmentation of the optical frequency band with the interruption ofcommunication services during operations of the communication services.As a result, it is impossible to resolve the fragmentation of theoptical frequency band; therefore, it is difficult to improve the usageefficiency of the optical frequency band.

As mentioned above, there has been a problem that, in an optical networkbased on a dense wavelength division multiplexing system using aflexible frequency grid, it is difficult to improve the usage efficiencyof an optical frequency band owing to the occurrence of fragmentation ofthe optical frequency band.

The object of the present invention is to provide an optical nodedevice, an optical network controller, and an optical network controlmethod to solve the problem mentioned above.

Solution to Problem

An optical network controller according to an exemplary aspect of thepresent invention includes an optical frequency region setting means fordividing an optical frequency band used in an optical network based on adense wavelength division multiplexing system using a flexible frequencygrid, and setting a plurality of optical frequency regions; and anoptical path setting means for setting optical paths having a commonattribute in at least one of the plurality of optical frequency regions.

An optical node device according to an exemplary aspect of the presentinvention includes an optical transmitting and receiving means fortransmitting and receiving an optical signal propagating through anoptical network based on a dense wavelength division multiplexing systemusing a flexible frequency grid; and a control means for setting acenter frequency and a bandwidth of the optical signal in the opticaltransmitting and receiving means so as to accommodate the optical signalin a specific optical path, wherein the control means selects thespecific optical path from among optical paths having a common attributethat are set in at least one of a plurality of optical frequency regionsobtained by dividing an optical frequency band used in the opticalnetwork.

An optical network system according to an exemplary aspect of thepresent invention includes an optical node device configured to be usedfor an optical network based on a dense wavelength division multiplexingsystem using a flexible frequency grid; and an optical networkcontroller, wherein the optical network controller includes an opticalfrequency region setting means for dividing an optical frequency bandused in the optical network and setting a plurality of optical frequencyregions, and an optical path setting means for setting optical pathshaving a common attribute in at least one of the plurality of opticalfrequency regions, the optical node device includes an opticaltransmitting and receiving means for transmitting and receiving anoptical signal propagating through the optical network, and a controlmeans for setting a center frequency and a bandwidth of the opticalsignal in the optical transmitting and receiving means so as toaccommodate the optical signal in a specific optical path, wherein thecontrol means selects the specific optical path from among optical pathshaving a common attribute that are set in at least one of the pluralityof optical frequency regions obtained by dividing the optical frequencyband used in the optical network.

An optical network control method according to an exemplary aspect ofthe present invention includes dividing an optical frequency band usedin an optical network based on a dense wavelength division multiplexingsystem using a flexible frequency grid, and setting a plurality ofoptical frequency regions; and setting optical paths having a commonattribute in at least one of the plurality of optical frequency regions.

Advantageous Effects of Invention

According to the optical node device, the optical network controller,and the optical network control method of the present invention, it ispossible to prevent the occurrence of fragmentation of an opticalfrequency band and improve the usage efficiency of the optical frequencyband in an optical network based on a dense wavelength divisionmultiplexing system using a flexible frequency grid.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of an opticalnetwork system in accordance with a first exemplary embodiment of thepresent invention.

FIG. 2 is a diagram schematically illustrating optical frequency regionsto be set by an optical network controller in accordance with the firstexemplary embodiment of the present invention.

FIG. 3 is a schematic diagram for describing an operation of the opticalnetwork controller in accordance with the first exemplary embodiment ofthe present invention.

FIG. 4 is a diagram schematically illustrating optical paths to beinitially set in optical frequency regions by the optical networkcontroller in accordance with the first exemplary embodiment of thepresent invention.

FIG. 5 is a diagram illustrating together the numbers of optical pathsthat can be set in optical frequency regions by the optical networkcontroller in accordance with the first exemplary embodiment of thepresent invention.

FIG. 6 is a diagram schematically illustrating a usage situation of anoptical frequency band in a comparative example with respect to theexemplary embodiments of the present invention.

FIG. 7 is a diagram illustrating together the numbers of optical pathsthat can be set in the comparative example with respect to the exemplaryembodiments of the present invention.

FIG. 8A is a schematic diagram for describing an operation of an opticalpath setting means included in an optical network controller inaccordance with a second exemplary embodiment of the present invention.

FIG. 8B is a schematic diagram for describing another operation of theoptical path setting means included in the optical network controller inaccordance with the second exemplary embodiment of the presentinvention.

FIG. 8C is a schematic diagram for describing yet another operation ofthe optical path setting means included in the optical networkcontroller in accordance with the second exemplary embodiment of thepresent invention.

FIG. 9 is a schematic diagram for describing another operation of theoptical path setting means included in the optical network controller inaccordance with the second exemplary embodiment of the presentinvention.

FIG. 10 is a diagram illustrating together the numbers of optical pathsthat can be set in optical frequency regions by the optical networkcontroller in accordance with the second exemplary embodiment of thepresent invention.

FIG. 11A is a table illustrating the numbers of optical paths that canbe set in optical frequency regions by the optical network controllersin accordance with the first exemplary embodiment and the secondexemplary embodiment of the present invention together with the case ofthe comparative example.

FIG. 11B is a diagram illustrating the numbers of optical paths that canbe set in optical frequency regions by the optical network controllersin accordance with the first exemplary embodiment and the secondexemplary embodiment of the present invention together with the case ofthe comparative example.

FIG. 12 is a diagram schematically illustrating optical paths set inoptical frequency regions by an optical network controller in accordancewith a third exemplary embodiment of the present invention.

FIG. 13 is a diagram schematically illustrating a usage situation of anoptical frequency band in the optical network controller in accordancewith the third exemplary embodiment of the present invention.

FIG. 14 is a diagram illustrating together the numbers of optical pathsset in optical frequency regions by the optical network controller inaccordance with the third exemplary embodiment of the present invention.

FIG. 15 is a diagram schematically illustrating a usage situation anoptical frequency band in a comparative example with respect to thethird exemplary embodiment of the present invention.

FIG. 16 is a schematic diagram for describing optical path setting inthe comparative example with respect to the third exemplary embodimentof the present invention.

FIG. 17 is a diagram illustrating together the numbers of optical pathsthat can be set in the comparative example with respect to the thirdexemplary embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the present invention will be described belowwith reference to the drawings.

A First Exemplary Embodiment

FIG. 1 is a block diagram illustrating a configuration of an opticalnetwork system 1000 in accordance with a first exemplary embodiment ofthe present invention.

The optical network system 1000 includes an optical network controller100 and an optical node device 200 that are used for an optical network300 based on a dense wavelength division multiplexing system using aflexible frequency grid.

The optical network controller 100 includes an optical frequency regionsetting means 110 and an optical path setting means 120. The opticalfrequency region setting means 110 divides an optical frequency bandused in the optical network 300 and sets a plurality of opticalfrequency regions. The optical path setting means 120 sets optical pathshaving a common attribute in at least one of the plurality of opticalfrequency regions.

The optical node device 200 includes an optical transmitting andreceiving means 210 and a control means 220. The optical transmittingand receiving means 210 transmits and receives an optical signalpropagating through an optical network. The control means 220 sets acenter frequency and a bandwidth of an optical signal in the opticaltransmitting and receiving means 210 so that the optical signal may beaccommodated in a specific optical path. Here, the control means 220selects the specific optical path from among optical paths having acommon attribute that are set in at least one of a plurality of opticalfrequency regions obtained by dividing an optical frequency band used inthe optical network 300.

In the optical network system 1000 according to the present exemplaryembodiment, the optical network controller 100 is configured to dividean optical frequency band in advance, set a plurality of opticalfrequency regions, and set optical paths having a common attribute in atleast one of the plurality of optical frequency regions. An opticalnetwork control method according to the present exemplary embodimentincludes, first, dividing an optical frequency band used in an opticalnetwork based on a dense wavelength division multiplexing system using aflexible frequency grid, and setting a plurality of optical frequencyregions. And it is configured to set optical paths having a commonattribute in at least one of the plurality of optical frequency regions.

Those configurations make it possible to prevent the occurrence offragmentation of an optical frequency band and improve the usageefficiency of the optical frequency band in an optical network.

The optical path setting means 120 can be configured to set each opticalpath having an attribute different from one another in each of aplurality of optical frequency regions.

Next, the operation of the optical network controller 100 according tothe present exemplary embodiment will be described in further detail.

A case will be described below as an example in which the optical pathsetting means 120 sets optical paths using the number of frequency slotscomposing an optical path as an attribute. Specifically, as to types ofoptical paths, an optical path with one slot in width, an optical pathwith two slots in width, and an optical path with four slots in widthare set.

In the optical network 300 illustrated in FIG. 1, “A” to “F” representnodes respectively. The optical node device 200 is disposed in eachnode, and optical fibers connect respective nodes to each other. Here,the optical network controller 100 is configured to notify each opticalnode device 200 of optical path setting information.

An optical fiber from the node A to the node C in the optical network300 will be described as an example. It is assumed that the entirety ofthe optical frequency region that can be transmitted through the opticalfiber complies with a flexible frequency grid standardized by ITU-Trecommendation G.694.1, and that the slot width of the flexiblefrequency grid is forty slots wide in total. FIG. 2 illustrates theentirety of the optical frequency region that can be transmitted throughthe optical fiber from the node A to the node C. The horizontal axisrepresents an optical frequency, and each rectangular block represents afrequency slot.

The optical frequency region setting means 110 included in the opticalnetwork controller 100 divides the optical frequency band and sets threeoptical frequency regions (bands 1 to 3), for example. A separator 1 anda separator 2 in FIG. 2 indicate an optical frequency forming thedivision between the bands. In the example illustrated in FIG. 2, theband 1 is an optical frequency region including twelve slots, the band 2is one including fourteen slots, and the band 3 is one includingfourteen slots.

Here, the optical path setting means 120 sets optical paths having acommon attribute in each of the optical frequency regions (bands),respectively. Accordingly, for example, if it is configured for the band1 to accommodate only an optical path with one slot in width, the band 1cannot accommodate an optical path with two slots in width and anoptical path with four slots in width that differ in the attribute eventhough there is an empty area. FIG. 3 schematically illustrates anoperation in this case.

As illustrated in FIG. 4, eight pieces of optical path one slot wide,five pieces of optical path two slots wide, and two pieces of opticalpath four slots wide are set as initial setting in the optical frequencyregions illustrated in FIG. 2.

It is considered to set additionally, in the optical frequency regionsin the initial state illustrated in FIG. 4, new optical paths totransmit an optical signal through the optical fiber from the node A tothe node C in the optical network 300 illustrated in FIG. 1. In thiscase, if it is possible to set additionally a large number of newoptical paths, the number of empty slots, in which no optical path isset, can be decreased, which makes it possible to increase the opticalfrequency usage efficiency.

In the example illustrated in FIG. 4, the number of empty slots is fourin the band 1, four in the band 2, and six in the band 3. In this case,the maximum number of addable optical paths is four in the band 1 foroptical path one slot wide, two in the band 2 for optical path two slotswide, and one in the band 3 for optical path four slots wide. Theseresults are illustrated together in FIG. 5.

Here, it will be considered as a comparative example to use a flexiblefrequency grid without dividing an optical frequency band by separators.In this case, there can be various usage situations of the opticalfrequency band in the optical fiber transmission line from the node A tothe node C in the optical network 300 illustrated in FIG. 1. An exampleof the usage situations is illustrated in FIG. 6.

In the example illustrated in FIG. 6, the number of empty slots is tenfor empty slot one slot wide, and two for empty slot two slots wide. Inthis case, two pieces of empty slot two slots wide can be regarded asfour pieces of empty slot one slot wide. Accordingly, if each of all theempty slots is used for an optical path one slot wide, it is possible toaccommodate up to fourteen optical paths. If maximum pieces of opticalpath two slots wide are accommodated, it is possible to accommodate twopieces of optical path two slots wide, and to accommodate ten pieces ofoptical path one slot wide. These results are illustrated together inFIG. 7.

In the comparative example illustrated in FIG. 6, it is impossible toaccommodate an optical path four slots wide. However, according to theoptical network controller 100 in the present exemplary embodiment, asillustrated in FIG. 4, it is possible to accommodate one optical pathfour slots wide. This is based on the effect that the optical networkcontroller 100 in the present exemplary embodiment prevents thefragmentation of the optical frequency band from occurring in theoptical fiber transmission line from the node A to the node C in theoptical network 300 illustrated in FIG. 1.

As described above, the optical network controller 100 in the presentexemplary embodiment makes it possible to accommodate an optical pathfour slots wide (a large granularity optical path), which has beenimpractical by the method of the comparative example. In the presentexemplary embodiment, it is unnecessary to use the defragmentationtechnique as described in Patent Literature 1.

A Second Exemplary Embodiment

Next, a second exemplary embodiment of the present invention will bedescribed. An optical network controller according to the presentexemplary embodiment includes an optical frequency region setting means110 and an optical path setting means 120. The optical frequency regionsetting means 110 divides an optical frequency band used in an opticalnetwork 300 and sets a plurality of optical frequency regions. Theoptical path setting means 120 sets optical paths having a commonattribute in at least one of the plurality of optical frequency regions.

The optical network controller according to the present exemplaryembodiment differs in the configuration of the optical path settingmeans 120 from the optical network controller 100 according to the firstexemplary embodiment. The optical path setting means 120 in the presentexemplary embodiment is configured to derive the number of frequencyslots from the sum of bandwidths of an electrical signal to generate anoptical signal to be accommodated in an optical path. That is to say,although the optical path setting means 120 according to the firstexemplary embodiment sets an optical path only by the multiplexing in anoptical domain, the optical path setting means 120 in the presentexemplary embodiment sets an optical path by using the multiplexing inan electrical domain together.

For example, the optical path setting means 120 according to the firstexemplary embodiment is configured to generate an optical path fourslots wide from an electrical signal having a bandwidth four slots wide.In contrast, the optical path setting means 120 in the present exemplaryembodiment is configured to generate an optical path four slots wide byperforming an electric-optic conversion on an electrical signal fourslots wide that is generated by electrically multiplexing a plurality ofelectrical signals, each of which has a bandwidth with a smaller slotwidth than four slots width.

As illustrated in FIG. 8A, a specific example can be configured togenerate an optical path four slots wide by performing an electric-opticconversion on an electrical signal four slots wide that is generated byelectrically multiplexing four electrical signals, each of which has abandwidth one slot wide. Alternatively, as illustrated in FIG. 8B,another specific example can be configured to generate an optical pathfour slots wide by performing an electric-optic conversion on anelectrical signal four slots wide that is generated by electricallymultiplexing two electrical signals, each of which has a bandwidth twoslots wide. Alternatively, as illustrated in FIG. 8C, yet anotherspecific example can be configured to generate an optical path two slotswide by performing an electric-optic conversion on an electrical signaltwo slots wide that is generated by electrically multiplexing twoelectrical signals, each of which has a bandwidth one slot wide.

In generating an optical signal four slots wide, it could be that thereis only one electrical signal one slot wide and that three pieces ofelectrical signal one slot wide are deficient. In this case, an opticalsignal four slots wide may be generated by adding three dummy signals orreplicating the electrical signal one slot wide. That is to say, forexample, as illustrated in FIG. 9, an optical signal (an optical path)four slots wide may be generated by performing an electric-opticconversion on an electrical signal four slots wide that is generated byelectrically multiplexing one electrical signal one slot wide and threepieces of dummy electrical signal one slot wide.

However, the above-mentioned electrical multiplexing can be applied onlyif all the electrical signals to be multiplexed are transmitted from theidentical node and are received by the identical node. It is excluded toseparate only a part of signals at an intermediary node or interchangedata, for example.

As mentioned above, the optical path setting means 120 in the presentexemplary embodiment is configured to use the multiplexing in anelectrical domain together. This makes it possible to accommodate asignal one slot wide also in the band 2 and band 3 by multiplexing,whereas the signal one slot wide can be accommodated only in the band 1by multiplexing signals only in the optical domain.

A specific example will be described based on the example illustrated inthe first exemplary embodiment (see FIG. 4). In the example illustratedin FIG. 4, the number of empty slots is four in the band 1, four in theband 2, and six in the band 3. In this case, the maximum number ofaddable optical paths is four in the band 1 for optical path one slotwide, two in the band 2 for optical path two slots wide, and one in theband 3 for optical path four slots wide. Using the electricalmultiplexing makes it possible to accommodate an electrical signal oneslot wide in each of all the addable optical paths. Accordingly, themaximum number of addable optical path one slot wide is twelve in total,that is, four in the band 1 (one slot×four), four in the band 2 (twoslots×two), and four in the band 3 (four slots×one). Similarly, themaximum number of addable optical path two slots wide is four in total,that is, zero in the band 1 because only an optical path one slot widecan be accommodated in the band 1, two in the band 2 (two slots×two),and two in the band 3 (two slots×two). These results are illustratedtogether in FIG. 10.

If the above results are compared with the results obtained by theoptical path setting means 120 in the first exemplary embodimentillustrated in FIG. 5, it is clear that the maximum number of addableallocation increases in the band 1 and the band 2. This is based on theeffect due to the configuration in which the electrical multiplexing isused together. As described above, using the electrical multiplexingtogether makes it possible to improve further the usage efficiency ofthe optical frequency band in the optical fiber transmission line fromthe node A to the node C in the optical network 300 illustrated in FIG.1.

If the results obtained by the optical path setting means 120 in thepresent exemplary embodiment illustrated in FIG. 10 are compared withthe results of the comparative example illustrated in FIG. 7, it isclear that the maximum number of addable allocation increases in theband 2 and the band 3. The above results are illustrated together inFIG. 11A and FIG. 11B.

A Third Exemplary Embodiment

Next, a third exemplary embodiment of the present invention will bedescribed. An optical network controller according to the presentexemplary embodiment includes an optical frequency region setting means110 and an optical path setting means 120. The optical frequency regionsetting means 110 divides an optical frequency band used in an opticalnetwork 300 and sets a plurality of optical frequency regions. Theoptical path setting means 120 sets optical paths having a commonattribute in at least one of the plurality of optical frequency regions.

The optical network controller according to the present exemplaryembodiment differs in the configuration of the optical path settingmeans 120 from the optical network controller 100 according to the firstexemplary embodiment. The optical path setting means 120 in the presentexemplary embodiment is configured to use a connection period of anoptical path as an attribute, and to set optical paths having a commonconnection period in at least one of the optical frequency regions.Specifically, a contract period during which an optical path staysconnected is used as the attribute of an optical path instead of thenumber of slots used in the first and second exemplary embodiments.

In general, the shorter a period during which an optical path staysconnected is, the higher the frequency of adding or deleting an opticalpath is. Accordingly, the fragmentation of the optical frequency band ismade likely. The optical network controller in the present exemplaryembodiment, however, makes it possible to prevent the occurrence of thefragmentation as will become apparent below.

In the present exemplary embodiment, as illustrated in FIG. 12, anoptical path with a connection period of one month is accommodated inthe band 1, an optical path with a connection period of one week isaccommodated in the band 2, and an optical path with a connection periodof one day is accommodated in the band 3, for example. In the band 1with the contract period equal to one month, three pieces of opticalpath one slot wide, two pieces of optical paths two slots wide, and oneoptical path four slots wide are accommodated. In the band 2 with thecontract period equal to one week, two pieces of optical path one slotwide, one optical path two slots wide, and two pieces of optical pathfour slots wide are accommodated. In the band 3 with the contract periodequal to one day, three pieces of optical path one slot wide, and twopieces of optical path two slots wide are accommodated.

FIG. 13 illustrates an example of the situation on a day when one dayhas passed since the day that the situation of the optical frequencyregion is illustrated in FIG. 12, and in the situation, optical pathshave been reconfigured in the band 3 with the contract period equal toone day. Specifically, the situation of the optical paths accommodatedin the band 3 changes from the situation where three pieces of opticalpath one slot wide and two pieces of optical path two slots wide areaccommodated to the situation where one optical path one slot wide, oneoptical path two slots wide, and two pieces of optical path four slotswide are accommodated. FIG. 14 illustrates together changes in thenumber of the optical paths allocated to the bands 1 to 3 from the firstday to the second day.

Here, it will be considered as a comparative example to use a flexiblefrequency grid without dividing an optical frequency band by separators.A usage situation of the optical frequency band in the initial state (onthe first day) in this case is assumed to be the situation illustratedin FIG. 15, for example. In this case, each number of optical pathshaving one slot, two slots, and four slots in width is the same as thatin the present exemplary embodiment illustrated in FIG. 12.

Next, the situation on the second day is considered when a period of oneday contract has passed among the contract periods for the optical pathconnection. The types of optical paths to be added or deleted are thesame as those in the present exemplary embodiment illustrated in FIG.13. In the case of the comparative example, however, if trying to deleteone optical path two slots wide and two pieces of optical path one slotwide, and add one optical path four slots wide, the number of addableoptical path four slots wide is limited to one, as illustrated in FIG.16. FIG. 17 illustrates together increases or decreases in optical pathsin the comparative example.

As is clear from comparison of FIG. 17 with FIG. 14, the number ofaddable optical path four slots wide decreases on the second day in thecomparative example. This shows that it is possible to prevent theoccurrence of fragmentation according to the present exemplaryembodiment. As a result, according to the optical network controller inthe exemplary embodiment, it is possible to improve the usage efficiencyof the optical frequency.

The above-mentioned exemplary embodiments are described in which thenumber of frequency slots composing an optical path, or a connectionperiod of an optical path is used as the attribute of the optical path.The present invention, however, is not limited to this. It is possibleto use the number of domains in the optical network through whichoptical paths pass, for example. Specifically, for example, it can beconsidered that the entire optical network is a group including a domain“a” of a subnetwork controlled by the operator A, a domain “b” of asubnetwork controlled by the operator B, and the like. In this case, anoptical path only within the domain “a”, an optical path only within thedomain “b”, and an optical path lying astride both in the domain “a” andthe domain “b” may be set in optical frequency regions different fromeach other, respectively. A use for an optical path, a person in chargeof operating an optical path, or the like may be used as the attributeof an optical path.

The present invention has been described by taking the exemplaryembodiments described above as model examples. However, the presentinvention is not limited to the aforementioned exemplary embodiments.The present invention can be implemented in various modes that areapparent to those skilled in the art within the scope of the presentinvention.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2014-089695, filed on Apr. 24, 2014, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   100 Optical network controller-   110 Optical frequency region setting means-   120 Optical path setting means-   200 Optical node device-   210 Optical transmitting and receiving means-   220 Control means-   300 Optical network-   1000 Optical network system

What is claimed is:
 1. An optical network controller, comprising: anoptical frequency region setting unit configured to divide an opticalfrequency band used in an optical network based on a dense wavelengthdivision multiplexing system using a flexible frequency grid, and set aplurality of optical frequency regions; and an optical path setting unitconfigured to set optical paths having a common attribute in at leastone of the plurality of optical frequency regions.
 2. The opticalnetwork controller according to claim 1, wherein the optical pathsetting unit sets each of the optical paths having an attributedifferent from one another in each of the plurality of optical frequencyregions.
 3. The optical network controller according to claim 1, whereinthe optical path setting unit sets the optical paths using number offrequency slots composing each of the optical paths as the attribute. 4.The optical network controller according to claim 3, wherein the opticalpath setting unit derives the number of frequency slots from a sum ofbandwidths of an electrical signal to generate an optical signal to beaccommodated in each of the optical paths.
 5. The optical networkcontroller according to claim 1, wherein the optical path setting unitsets the optical paths using a connection period of the optical paths asthe attribute.
 6. An optical node device, comprising: an opticaltransmitting and receiving unit configured to transmit and receive anoptical signal propagating through an optical network based on a densewavelength division multiplexing system using a flexible frequency grid;and a control unit configured to set a center frequency and a bandwidthof the optical signal in the optical transmitting and receiving unit soas to accommodate the optical signal in a specific optical path, whereinthe control unit selects the specific optical path from among opticalpaths having a common attribute that are set in at least one of aplurality of optical frequency regions obtained by dividing an opticalfrequency band used in the optical network.
 7. The optical node deviceaccording to claim 6, wherein the optical paths have in common number offrequency slots composing each of the optical paths.
 8. The optical nodedevice according to claim 6, wherein the optical paths have a connectionperiod of each of the optical paths in common.
 9. An optical networksystem, comprising: the optical network controller according to claim 1;and an optical node device configured to be used for an optical networkbased on a dense wavelength division multiplexing system using aflexible frequency grid; wherein the optical node device includes anoptical transmitting and receiving unit configured to transmit andreceive an optical signal propagating through the optical network, and acontrol unit configured to set a center frequency and a bandwidth of theoptical signal in the optical transmitting and receiving unit so as toaccommodate the optical signal in a specific optical path, wherein thecontrol unit selects the specific optical path from among optical pathshaving a common attribute that are set in at least one of the pluralityof optical frequency regions obtained by dividing the optical frequencyband used in the optical network.
 10. An optical network control method,comprising: dividing an optical frequency band used in an opticalnetwork based on a dense wavelength division multiplexing system using aflexible frequency grid, and setting a plurality of optical frequencyregions; and setting optical paths having a common attribute in at leastone of the plurality of optical frequency regions.
 11. The opticalnetwork control method according to claim 10, wherein the setting of theoptical paths includes setting each of the optical paths having anattribute different from one another in each of the plurality of opticalfrequency regions.
 12. The optical network control method according toclaim 10, wherein the setting of the optical paths includes setting theoptical paths using number of frequency slots composing each of theoptical paths as the attribute.
 13. The optical network control methodaccording to claim 12, wherein the setting of the optical paths includesderiving the number of frequency slots from a sum of bandwidths of anelectrical signal to generate an optical signal to be accommodated ineach of the optical paths.
 14. The optical network control methodaccording to claim 10, wherein the setting of the optical paths includessetting the optical paths using a connection period of the optical pathsas the attribute.
 15. The optical network controller according to claim2, wherein the optical path setting unit sets the optical paths usingnumber of frequency slots composing each of the optical paths as theattribute.
 16. The optical network controller according to claim 2,wherein the optical path setting unit sets the optical paths using aconnection period of the optical paths as the attribute.
 17. The opticalnetwork control method according to claim 11, wherein the setting of theoptical paths includes setting the optical paths using number offrequency slots composing each of the optical paths as the attribute.18. The optical network control method according to claim 11, whereinthe setting of the optical paths includes setting the optical pathsusing a connection period of the optical paths as the attribute.